Rice (Oryza sativa L.) is one of the major staple food source for more than half of the global population. To attain the food needs of the world’s growing population, further increase in rice productivity is needed. To assess the sensitivity of agricultural output, a greater comprehension of the possible interactions amongst crops and weeds in the face of climate change, especially under elevated CO2 (EC) and elevated temperature (ET), is essential. This study was conducted to quantify the influence of elevated temperature, CO2, weed density and their interactions on crop-weed competition, rice yield parameters and grain yield. The experiment was conducted in four separate Open Top Chambers (OTCs), viz. with ambient CO2 (A), elevated CO2 [550±50 ppm] (EC), elevated temperature (ambient±2 °C) (ET) and combined effect of elevated CO2 and temperature (EC+ET) with and without weed competition. The EC alone enhanced the rice grain yield by 42.30% in weed-free conditions when compared to ambient CO2, however substantial change was not observed under ET. In the EC+ET condition, however, regardless of weeds presence or absence, crop output was reduced by 22.02 percent. Alternanthera paronychioides A. St.-Hil. competition caused rice yield reduction of 79.72, 83.04, 62.98 and 62.01% at A, EC, ET, EC+ET, respectively. The EC and ET interactions will certainly exert a profound influence on weed growth and competition against crops, which ultimately enhances crop yield losses in futuristic climate change scenario.